Recording and reproducing apparatus for detecting the presence or absence of a copy guard to prevent false processing of noise signals

ABSTRACT

A video signal recording and/or reproducing apparatus includes a copy guard processing detecting current which can correctly judge whether or not a copy guard is applied to an input video signal and prevents copy guard processing from being applied to a video signal to which a copy guard is not applied. The copy guard processing detecting apparatus includes a first circuit for receiving an input video signal which includes a plurality of false synchronizing signals for prevention of duplication inserted in a vertical blanking interval thereof and for counting the number of the false synchronizing signals, a second circuit for counting the number of synchronizing signals in an image interval of the input video signal except the vertical blanking interval, a discriminating circuit for discriminating whether or not copy guard processing is applied to the input video signal from the count values of the first and second circuits, and a recording system for receiving and recording the input video signal based on the results of the copy guard discriminating operation.

This is a division of application Ser. No. 08/004,942, filed Jan. 15,1993, now U.S. Pat. No. 5,337,157.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a copy guard processing detecting apparatusfor detecting whether or not a video signal of a recorded video tape onwhich a piece of video software such as a motion picture is recorded isprocessed for prevention of duplication of itself.

2. Description of the Related Art

It is a popular practice, in order to make it substantially impossibleto copy or duplicate a recorded tape, on which a piece of video softwaresuch as a motion picture is recorded, by means of a video tape recorderfor home use, to apply some processing to the recorded video signal forprevention of duplication of the signal itself (such processing will behereinafter referred to as copy guard).

An exemplary one of conventional copy guard methods is disclosed inJapanese Patent Laid-Open Application No. 61-288582 and is popularlyused. According to the method, a plurality of pairs of pulses eachincluding a false synchronization pulse and a positive pulse areinserted in each vertical blanking interval, and an AGC (automatic gaincontrol) circuit of the recording system of a predeterminedcharacteristic is utilized for processing with a copy guard. The reasonwhy a signal for a copy guard is inserted in a vertical blankinginterval is that the signal for a copy guard may possibly have a badinfluence on contents themselves of a piece of video software otherwiseif it is inserted directly into an image signal interval.

FIG. 4 illustrates the copy guard method disclosed in the documentmentioned above. The waveform B in FIG. 4 shows an example of a videosignal wherein a plurality of pairs of pulses each including a falsesynchronization pulse and a positive pulse for a copy guard (such pairsof pulses will be hereinafter referred to as copy guard signal) areinserted in a vertical blanking interval. Meanwhile, the waveform A inFIG. 4 shows another video signal which does not include such pulsesinserted therein. In the video signal shown by the waveform of FIG. 4,five pairs of pulses each including a false synchronization pulse DP anda positive pulse LP are inserted for each fixed period in each ofhorizontal intervals from the thirteenth to eighteenth horizontalintervals in a vertical blanking interval of an odd-numbered field.

It is to be noted that, in the case of the video signal shown by thewaveform B of FIG. 4, though not shown, another copy guard signal isinserted similarly between the 275th to 280th horizontal intervals of aneven-numbered field.

In the video signal of the waveform B of FIG. 4, a rising edge of afalse synchronization pulse DP continues to a rising edge of a nextpositive pulse LP, and accordingly, if the copy guard signal is insertedin the video signal, an AGC circuit of the recording system of a videotape recorder will determine that a synchronization pulse has amagnitude equal to the magnitude from a peak value of the falsesynchronization pulse DP to a peak value of the positive pulse LP andaccordingly will effect gain control as if the level of the input videosignal is as high as, for example, three times or more a standard level.Consequently, if the recorded signal is reproduced, then since it hasbeen attenuated to a level equal to or less than 30% of the standardlevel, only an unstable image of a low quality can be obtained. In otherwords, a copy guard can substantially be achieved.

Also it is a common practice to change the level of such positive pulsesLP suitably to change the AGC level to various values in order tofurther deteriorate the quality of the reproduced image.

Since the conventional copy guard coping processing relies on a peculiarcharacteristic of an AGC circuit of a video tape recorder with regard toan external input, the copy guard function cannot sometimes be obtainedsufficiently depending upon the type, the characteristic or theperformance of the AGC circuit.

Further, since the conventional copy guard method does not cause the AGCcircuit to operate in accordance with a result of judgment whether ornot a copy guard is actually applied to a video signal, it has adrawback that the AGC circuit reacts with a noise which is generatedwhen, for example, tracking is lost or variable speed reproduction isperformed with the video tape recorder or with some other disturbancenoise taking the noise as a false pulse so that the video signal to berecorded is deteriorated to a low quality although the video signal isoriginally a normal video signal.

The drawback arises from the fact that the copy guard coping processingfunction is normally put into an operating condition whether or not acopy guard is applied to a video signal.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a copy guardprocessing detecting apparatus which can correctly judge whether or nota copy guard is applied to an input video signal.

It is another object of the present invention to provide a copy guardprocessing detecting apparatus which prevents processing with a copyguard from being applied to a video signal to which a copy guard is notapplied.

In order to attain the objects, according to the present invention,there is provided a copy guard processing detecting apparatus, whichcomprises first means for receiving an input video signal which includesa plurality of false synchronizing signals for prevention of duplicationinserted in a vertical blanking interval thereof and for counting thenumber of the false synchronizing signals, second means for counting thenumber of synchronizing signals in an image interval of the input videosignal except the vertical blanking interval, and discriminating meansfor discriminating whether or not copy guard processing is applied tothe input video signal from the count values of the first and secondmeans.

With the copy guard processing detecting apparatus, the discriminatingmeans discriminates that a copy guard is applied correctly to the inputvideo signal when the count value of the second means indicates that nonoise is included in the image interval of the input video signal andthe count value of the first means indicates that copy guard processingis applied to the input video signal.

In particular, even if the count value of the first means indicates thata number of pulses greater than a number determined in advance for falsesynchronizing signals are involved in the vertical blanking interval ofthe input video signal and accordingly copy guard processing is appliedto the input video signal, when the count value of the second meansindicates that noises are involved in the image interval so that anumber of synchronizing pulses greater than a predetermined number areinvolved in the image interval, the discriminating means determines thata copy guard is not applied to the input video signal. This is becausethe probability is high that the false synchronizing pulses detected ascopy guard signals in the vertical blanking interval are not copy guardpulses but are noises.

Accordingly, with the copy guard processing detecting apparatus, sincepresence of false synchronizing pulses for a copy guard inserted in avertical blanking interval is detected to detect whether or not copyguard processing is applied to the video signal, appropriate copy guardcoping processing can be applied to the video signal and also to anincidental audio signal using the detection output of the copy guardprocessing detecting apparatus.

Furthermore, since whether or not copy guard processing is applied to avideo signal is detected not only by detection of presence of falsesynchronization pulses in a vertical blanking interval but also bychecking the number of synchronizing pulses in an image portion intervalto detect whether or not the false synchronizing signals in the videoblanking interval of the video signal are noises which are generatedupon variable speed reproduction of the video tape recorder or the like,presence or absence of copy guard processing can be detected accurately.

The above and other objects, features and advantages of the presentinvention will become apparent from the following description and theappended claims, taken in conjunction with the accompanying drawings inwhich like parts or elements are denoted by like reference characters.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a copy guard processing detecting apparatusshowing a preferred embodiment of the present invention;

FIG. 2 is a waveform diagram illustrating operation of the copy guardprocessing detecting apparatus of FIG. 1;

FIG. 3 is a block diagram of a double deck video tape recorder systemillustrating an exemplary application of the copy guard processingdetecting apparatus shown in FIG. 1; and

FIGS. 4A and 4B are waveform diagrams illustrating an example of asignal for copy guard processing.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring first to FIG. 1, there is shown a copy guard processingdetecting apparatus to which the present invention is applied. The copyguard processing detecting apparatus shown is generally denoted at 100and has an input terminal 1. A video signal inputted to the apparatus100 by way of the input terminal 1 is supplied to a synchronizingseparator circuit 2, from which a horizontal synchronizing signal H anda vertical synchronizing signal V are obtained. The synchronizingsignals H and V are supplied to a discrimination interval signalgenerating circuit 3 for the number of horizontal synchronizing pulses,a copy guard signal inserted portion synchronization detecting circuit4, and an image portion synchronization detecting circuit 5.

The discrimination interval signal generating circuit 3 produces, fromthe horizontal synchronizing signal H and the vertical synchronizingsignal V, as shown in FIG. 2, a window pulse SA which presents, forexample, the high level only for an interval (into which a copy guardsignal can be inserted) PA within a vertical blanking interval except 9horizontal intervals including equalizing pulse intervals and a verticalsynchronizing pulse interval, and another window pulse SB which presentsthe high level only for an image portion interval PB except a verticalblanking interval.

For example, in the case of an odd-numbered field of a video signal ofthe NTSC system, the interval PA includes the 10th to 21st horizontalintervals while the interval PB includes, for example, the 22nd to 263rdhorizontal intervals. On the other hand, in the case of an even-numberedfield, the interval PA includes the 272nd to 283rd horizontal intervalswhile the interval PB includes, for example, the 284th to 525thhorizontal intervals.

The window pulse SA is supplied to the copy guard signal insertedportion synchronization detecting circuit 4, at which the numbers ofsynchronizing pulses are counted for the interval PA. The copy guardsignal inserted portion synchronization detecting circuit 4 can beconstructed, for example, from a counter and a discriminating sectionwhich makes such a discrimination as will be hereinafter described inaccordance with an output count value of the counter, or alternativelymay be constructed from a microcomputer.

In this instance, since the interval PA has the width of elevenhorizontal intervals, if no copy guard signal is inserted in the videosignal, then normally eleven synchronizing pulses are detected. However,taking an error of the circuit system, a damage to the tape and so forthinto consideration, a margin α1 is set for the detected number ofhorizontal synchronizing pulses. The value of the margin may range, forexample, α1=2 to 4.

When the detected number N of synchronization pulses is N≦11+α1, thecopy guard signal inserted portion synchronization detecting circuit 4determines that the input video signal includes no copy guard signal,and puts the output DA thereof into a low level. On the other hand, ifthe detected number N of synchronizing pulses is N>11+α1, then the copyguard signal inserted portion synchronization detecting circuit 4determines that the input video signal includes a copy guard signal, andputs the output DA thereof into a high level. The state of the output DAof the circuit 4 is maintained for the interval of one field.Accordingly, if the determination for a certain field is the same asthat for the preceding field, then the state of the output DA maintainsthe condition then, but when the determination is different from thatfor the preceding field, then the state of the output DA is reversed.

On the other hand, the pulse SB from the discrimination interval signalgenerating circuit 3 is supplied to the image portion synchronizationdetecting circuit 5, at which the numbers of synchronizing pulses arecounted for the interval PB. Also the image portion synchronizationdetecting circuit 5 can be constructed from a counter and adiscriminating section which makes such a discrimination as will behereinafter described in accordance with an output count value of thecounter, or alternatively may be constructed from a microcomputer.

In this instance, since the interval PB has the width of 241 horizontalintervals, if no noise or no dropout is included in the video signal,then normally 241 synchronizing pulses are detected. However, taking anerror of the circuit system, a damage to the tape and so forth intoconsideration, a margin α2 is set for the detected number of horizontalsynchronizing pulses. The value α2 of the margin may be set, forexample, to ten or more or so.

When the detected number M of synchronization pulses is 241-α2≦M≦241+α2,the image portion synchronization detecting circuit 5 determines thatthe input video signal includes no noise and is normal, and puts theoutput DB thereof into the high level. On the other hand, if thedetected number M of synchronizing pulses is M>241+α2 or M<241-α2, thenthe image portion synchronization detecting circuit 5 determines thatthe input video signal includes a noise and is not a normal videosignal, and puts the output DB thereof into the low level. The state ofthe output DB of the circuit 5 is maintained for the interval of onefield. Accordingly, if the determination for a certain field is the sameas that for the preceding field, then the state of the output DBmaintains the condition then, but when the determination is differentfrom that for the preceding field, then the state of the output DB isreversed.

The output DA of the copy guard signal inserted portion synchronizationdetecting circuit 4 and the output DB of the image portionsynchronization detecting circuit 5 are supplied to an AND circuit 6.Accordingly, when the input video signal has a normal image portion anda copy guard signal is involved in the interval PA, the output of theAND circuit 6 presents the high level, but in any other case, the outputpresents the low level.

The output of the AND circuit 6 is supplied to a chattering preventingtime constant circuit 7. The time constant circuit 7 is provided to makedetection of a copy guard sure and outputs an output DET which presents,for example, the high level when the output of the AND circuit 6maintains the high level condition continuously for, for example, 30 to90 seconds. The output DET of the time constant circuit 7 makes theoutput of the copy guard processing detecting circuit 100.

In response to the output DET, copy guard coping processing is performedfor the input video signal. In particular, the input video signal issupplied to a copy guard coping processing circuit 8 while also theoutput DET of the copy guard processing detecting apparatus 100 issupplied to the copy guard coping processing circuit 8. The copy guardcoping processing circuit 8 effects copy guard coping processing for theinput video signal only when the output DET presents the high level.

In this instance, the coping processing may be, for example, to mute theinput video signal so that the input video signal is prevented frombeing outputted from the coping processing circuit 8, to attenuate thelevel of the input video signal, or to apply digital processing so thata regular reproduced image cannot be derived from the input video signalsuch as mosaic processing. Or otherwise, the video tape recorder may beconstructed such that the AGC circuit of the recording system for avideo signal is constructed to be changed over between a characteristicwherein the AGC circuit reacts effectively with a copy guard signal andanother characteristic wherein the AGC circuit is not influenced by acopy guard signal and is changed over, only when the output DET inputtedthereto has the high level, to the characteristic wherein the AGCcircuit reacts effectively with a copy guard signal so that an enjoyablereproduced image cannot be obtained. Or alternatively, the output DETmay be used such that the recording mode of the video tape recorder iscancelled when the output DET presents the high level.

Or else, the processing may be applied not only to a video signal butalso to an audio signal such that, only when the output DET presents thehigh level, muting processing or such processing as attenuation of thelevel, addition of noises which makes it difficult to enjoy soundderived from the audio signal, is applied.

Thus, when the output DET of the copy guard processing detectingapparatus 100 presents the low level, the processing described above isnot performed at the copy guard processing circuit 8 and the input videosignal is outputted as it is from the circuit 8.

The video signal and the audio signal from the processing circuit 8 aresupplied, for example, to the recording system of a video tape recorder.Consequently, when the output DET of the copy guard processing detectingapparatus 100 indicates that a copy guard is applied to the input videosignal, the video signal and/or the audio signal are prevented frombeing recorded without any processing applied thereto.

The output DET of the time constant circuit 7 is supplied also to analarming circuit 9 so that, when it is detected that a copy guard isapplied to the input video signal, the alarming circuit 9 notifies theuser of this by way of such means as, for example, lighting of analarming lamp, display by means of a display unit, or generation ofalarming sound. The user is thus prevented from mistaking that the videotape recorder fails.

Subsequently, an exemplary application of the copy guard processingdetecting apparatus according to the present invention will be describedwith reference to FIG. 3 in which the copy guard processing detectingapparatus is applied to a double deck video tape recorder system whichhas functions of two video tape recorders.

The double deck video tape recorder system includes a first video taperecorder section 11 for, for example, the VHS system and a second videotape recorder section 21 for, for example, the 8 mm video system.

The double deck video tape recorder system further includes a modechanging over signal generating circuit 31 to which an operation inputdecode signal is supplied from an operation input decoding circuit 33. Aremote control signal from a commander 34 for remote control is suppliedto the operation input decoding circuit 33, and also a key inputoperation signal from a key inputting operating section 35 is suppliedto the operation input decoding circuit 33. Accordingly, a mode changingover signal for putting the double deck video tape recorder system intoa mode corresponding to a remote control input from the commander 34 ora key inputting operation at the key inputting operating section 35 isdelivered from the mode changing over signal generating circuit 31.

An output video signal of the first video tape recorder section 11 andan output video signal of the second video tape recorder section 21 aresupplied to input terminals a and b of a switch circuit 30,respectively. The switch circuit 30 is switched alternatively to theinput a or b in response to a changing over signal SW from the modechanging over signal generating circuit 31 so that a selected one of theoutput video signals of the first and second video tape recordersections 11 and 21 is obtained from the switch circuit 30. The videosignal obtained from the switch circuit 30 is led out to a monitoroutput terminal 32. A video input terminal of a monitor televisionreceiver is connected to the monitor output terminal 32.

The double deck video tape recorder system further includes a pair ofinput select circuits 12 and 22 for the first and second video taperecorder sections 11 and 21, respectively. A video signal from a tuner36, an external input video signal from a line input terminal 37 and anoutput video signal of the second video tape recorder section 21 areinputted to the input select circuit 12. Meanwhile, a video signal fromthe tuner 36, an external input video signal from the line inputterminal 37 and an output video signal of the first video tape recordersection 11 are inputted to the input select circuit 22. A televisionantenna 38 is connected to the tuner 36.

Each of the input select circuits 12 and 22 presents an input selectingcondition in accordance with a mode set in response to a select signalfrom the mode changing over signal generating circuit 31.

Output signals of the input select circuits 12 and 22 are inputted tothe recording systems not shown of the first and second video taperecorder sections 11 and 21 by way of a pair of copy guard processingcircuits 13 and 23, respectively, each of which corresponds to thecircuit 8 of the apparatus described hereinabove with reference toFIG. 1. In the present double deck video tape recorder system, the copyguard processing is, for example, muting processing.

The output video signals of the input select circuits 12 and 22 aresupplied also to a pair of copy guard processing detecting circuits 14and 24, respectively, which each has the same construction as the copyguard processing detecting apparatus 100 described hereinabove withreference to FIG. 1. Accordingly, when a copy guard is applied to thevideo signal from the input select circuit 12 or 22, this is detected bythe detecting circuit 14 or 24, and such copy guard coping processing asdescribed above such as muting is performed at the coping processingcircuit 13 or 23 in accordance with the detection output DET of thedetecting circuit 14 or 24. The video signal to which such copy guardprocessing has been applied is supplied to the recording system of thevideo tape recorder section 11 or 21. Consequently, the copy guard actseffectively. In particular, the video signal from the input selectcircuit 12 or 22 is muted and is not supplied to the video tape recordersection 11 or 21, and consequently, dubbing of the input signal is notperformed.

In the double deck video tape recorder system of the constructiondescribed above, in any one of a case wherein the first video taperecorder section 11 is put into a reproducing condition and the secondvideo tape recorder section 21 is put into a recording condition inorder to effect so-called dubbing, another case wherein the second videotape recorder section 21 is put into a reproducing condition and thefirst video tape recorder section 11 is put into a recording conditionin order to effect dubbing and a further case wherein a video signalobtained by reproduction with an external video tape recorder issupplied to the line input terminal in order to record the video signalwith the first video tape recorder section 11 or the second video taperecorder section 21 to effect dubbing, the detecting circuit 14 or 24can detect accurately with certainty whether or not a copy guard isapplied to the reproduced video signal. In accordance with the detectionoutput of the detecting circuit 14 or 24, copy guard coping processingsuch as muting, attenuation of the recording level, stopping ofrecording or digital mosaic processing is performed appropriately.

It is to be noted that, while, in the double deck video tape recordersystem described above, a copy guard processing detecting circuit and acopy guard processing circuit are provided at the input stage of therecording system of each of the video tape recorder sections, the copyguard processing detecting circuit and the copy guard processing circuitmay otherwise be provided at the output stage of the reproducing systemof each video tape recorder section such that, when dubbing is to beperformed between the first video tape recorder section and the secondvideo tape recorder section, the copy guard processing detecting circuitof that one of the video tape recorder sections which is to be put intoa reproducing condition is enabled.

It is to be noted that, while the foregoing relates to copy guardprocessing for a video signal which involves insertion of one or aplurality of pairs of pulses each including a false synchronizing pulseand a positive pulse as a copy guard signal into a vertical blankinginterval, the copy guard processing as an object of the presentinvention is not limited to such specific processing but can be appliedto any video signal which includes a plurality of false synchronizingpulses in a vertical blanking interval thereof.

Having now fully described the invention, it will be apparent to one ofordinary skill in the art that many changes and modifications can bemade thereto without departing from the spirit and scope of theinvention as set forth herein.

What is claimed is:
 1. A video signal recording and/or reproducingcircuit comprising:an input terminal for receiving an input videosignal; a copy guard processing detecting circuit comprisingfirst meansfor receiving the input video signal which includes a plurality of falsesynchronizing signals for prevention of duplication inserted in avertical blanking interval thereof and for counting a number of thefalse synchronizing signals, second means for counting a number ofsynchronizing signals in an image interval of the input video signalexcept the vertical blanking interval, and discriminating means fordiscriminating whether or not a copy guard processing is applied to theinput video signal from count values of said first and second means andfor outputting a discriminated signal; and a recording system forreceiving and recording the input video signal.
 2. A video signalrecording and/or reproducing circuit according to claim 1, wherein saiddiscriminating means includes a time constant circuit for detecting thata condition wherein copy guard processing is applied to the input videosignal continues for a predetermined period of time.
 3. A video signalrecording and/or reproducing circuit according to claim 1, wherein saiddiscriminating means discriminates that copy guard processing is appliedto the input video signal when a count value of said first means isgreater than a sum of a predetermined number of false synchronizingsignals which must be included in the vertical blanking interval and amargin value.
 4. A video signal recording and/or reproducing circuitaccording to claim 1, wherein said discriminating means discriminatesthat the input video signal includes no noise therein when a count valueof said second means is greater than a difference of a margin value froma predetermined number of synchronizing signals which are to be includedin the image interval but is smaller than a sum of the margin value andthe predetermined number.
 5. A video signal recording and/or reproducingcircuit according to claim 1, further comprising an alarming circuit fornotifying a user that a copy guard is applied to the input video signalwhen said discriminating means determines that a copy guard signalprocessing is applied to the input video signal.
 6. A video signalrecording and/or reproducing circuit according to claim 1, furthercomprising a copy guard processing circuit for receiving the input videosignal and the discriminated signal and for processing the input videosignal when said discriminated means determines that a copy guard signalprocessing is applied to the input video signal.
 7. A video signalrecording and/or reproducing circuit according to claim 6, wherein saidprocessing of the input video signal by said copy guard processingcircuit comprises muting the input video signal.
 8. A video signalrecording and/or reproducing circuit according to claim 6, wherein saidprocessing of the input video signal by said copy guard processingcircuit comprises attenuating the input video signal.
 9. A video signalrecording and/or reproducing circuit according to claim 6, wherein saidprocessing of the input video signal by said copy guard processingcircuit comprises digital mosaic processing.
 10. A video signalrecording and/or reproducing circuit according to claim 6, wherein saidprocessing of the input video signal by said copy guard processingcircuit comprises the addition of extraneous noises to the input videosignal.
 11. A video signal recording and/or reproducing apparatuscomprising:an input terminal for receiving an input video signal; a copyguard processing detecting circuit comprisingfirst means for receivingthe input video signal which includes a plurality of false synchronizingsignals for prevention of duplication inserted in a vertical blankinginterval thereof and for counting a number of the false synchronizingsignals, second means for counting a number of synchronizing signals inan image interval of the input video signal except the vertical blankinginterval, and discriminating means for discriminating whether or not acopy guard processing is applied to the input video signal from countvalues of said first and second means and for outputting a discriminatedsignal; a copy guard coping processing circuit for receiving the inputvideo signal and the discriminated signal, for processing the inputvideo signal when said discriminated means determines that a copy guardsignal processing is applied to the input video signal, and foroutputting a processed signal; a recording system for receiving andrecording the processed signal and for outputting an output signal,wherein a recording of the processed signal is prevented when saiddiscriminating means determines that a copy guard signal processing isapplied to the input video signal; and a monitor output terminal forreceiving said output signal and feeding said output signal to amonitor.
 12. A video signal recording and/or reproducing apparatusaccording to claim 11, wherein said discriminating means includes a timeconstant circuit for detecting that a condition wherein copy guardprocessing is applied to the input video signal continues for apredetermined period of time.
 13. A video signal recording and/orreproducing apparatus according to claim 11, wherein said discriminatingmeans discriminates that copy guard processing is applied to the inputvideo signal when a count value of said first means is greater than asum of a predetermined number of false synchronizing signals which mustbe included in the vertical blanking interval and a margin value.
 14. Avideo signal recording and/or reproducing apparatus according to claim11, wherein said discriminating means discriminates that the input videosignal includes no noise therein when a count value of said second meansis greater than a difference of a margin value from a predeterminednumber of synchronizing signals which are to be included in the imageinterval but is smaller than a sum of the margin value and thepredetermined number.
 15. A video signal recording and/or reproducingapparatus according to claim 11, further comprising an alarming circuitfor notifying a user that a copy guard is applied to the input videosignal when said discriminating means determines that a copy guardsignal processing is applied to the input video signal.
 16. A videosignal recording and/or reproducing system comprising:a first videosignal recording and/or reproducing apparatus for outputting a firstoutput signal; a second video signal recording and/or reproducingapparatus connected to said first video signal recording and/orreproducing apparatus for outputting a second output signal; a switchcircuit including a first input terminal and a second input terminal forreceiving the first output signal and the second output signal,respectively, and an output terminal for outputting a third outputsignal; a mode changing over signal generating circuit connected to saidswitch circuit for supplying said switch circuit with a mode changingover signal for switching said switch circuit to one of the first inputterminal and the second input terminal in response to an operation inputdecode signal supplied to said mode changing over signal generatingcircuit, so that one of the first output signal and the second outputsignal is fed to the output terminal; and a monitor output terminal forreceiving and outputting the third output signal wherein each of saidfirst and second video signal recording and/or reproducing apparatusfurther comprises a copy guard detecting circuit includingdiscriminating means for discriminating whether a copy guard processingis applied to an input video signal fed thereto and for outputting adiscriminated signal, and a copy guard processing circuit receiving theinput video signal and the discriminated signal for processing the inputvideo signal when said discriminating means determines that a copy guardsignal processing is applied to the input video signal and outputting arespective processed output signal as one of said first and secondoutput signals fed to said switch circuit.
 17. A video signal recordingand/or reproducing system according to claim 16, wherein each of saidfirst video signal recording and/or reproducing apparatus and saidsecond video signal recording and/or reproducing apparatus furthercomprisesan input select circuit for selecting said input video signalfrom a plurality of input video signals; said copy guard detectingcircuit further includes first means for receiving from said inputselect circuit the selected input video signal which includes aplurality of false synchronizing signals for prevention of duplicationinserted in a vertical blanking interval thereof and for counting anumber of the false synchronizing signals, second means for counting anumber of synchronizing signals in an image interval of the selectedinput video signal except the vertical blanking interval; and arecording system for receiving and recording the processed signal andfor outputting the first output signal for said first video signalrecording and/or reproducing apparatus and the second output signal forsaid second video signal recording and/or reproducing apparatus,respectively, wherein a recording of the processed signal is preventedwhen said discriminating means determines that a copy guard signalprocessing is applied to the input video signal.
 18. A video signalrecording and/or reproducing system according to claim 17, furthercomprising a tuner connected to said input select circuits and a lineinput terminal connected to said input select circuits, wherein theplurality of input signals comprise a video signal from said tuner, anexternal input video signal from said line input terminal, and one ofthe second output signal for said first video signal recording and/orreproducing apparatus and the first output signal for said second videosignal recording and/or reproducing apparatus, respectively.
 19. A videosignal recording and/or reproducing circuit according to claim 18,wherein said mode changing over signal generating circuit generates aselect signal fed to said input select circuits for controlling aselection of one of said plurality of input signals for each of saidinput select circuits.
 20. A video signal recording and/or reproducingsystem according to claim 16, further comprising a monitor televisionreceiver connected to said monitor output terminal for receiving thethird output signal.
 21. A video signal recording and/or reproducingsystem according to claim 16, further comprising an operation inputdecoding circuit connected to said mode changing over signal generatingcircuit for receiving an input decoding signal and outputting anoperation input decoding signal to control said mode changing oversignal generating circuit.
 22. A video signal recording and/orreproducing system according to claim 21, further comprising a remotecontrol commander wherein the input decoding signal comprises a remotecontrol signal supplied by said remote control commander.
 23. A videosignal recording and/or reproducing system according to claim 21,further comprising a key inputting operating section wherein the inputdecoding signal comprises a key inputting operation signal supplied bysaid key inputting operating section.
 24. A video signal recordingand/or reproducing method comprising the steps of:receiving an inputvideo signal which includes a plurality of false synchronizing signalsfor prevention of duplication inserted in a vertical blanking intervalthereof; counting a number of the false synchronizing signals; countinga number of synchronizing signals in an image interval of the inputvideo signal except the vertical blanking interval; discriminatingwhether or not a copy guard processing is applied to the input videosignal from count values of the counting steps; and recording the inputvideo signal.
 25. A video signal recording and/or reproducing methodaccording to claim 24, further comprising the step of copy guardprocessing the input video signal after the discriminating step when itis determined that a copy guard signal processing is applied to theinput video signal.
 26. A video signal recording and/or reproducingmethod according to claim 24, further comprising the step of detectingthat a condition wherein copy guard processing is applied to the inputvideo signal continues for a predetermined period of time after thediscriminating step.
 27. A video signal recording and/or reproducingmethod according to claim 24, wherein the discriminating step determinesthat copy guard processing is applied to the selected input video signalwhen a count value of the first counting step is greater than a sum of apredetermined number of false synchronizing signals which must beincluded in the vertical blanking interval and a margin value.
 28. Avideo signal recording and/or reproducing method according to claim 24,wherein the discriminating step determines that the selected input videosignal includes no noise therein when a count value of the secondcounting step is greater than a difference of a margin value from apredetermined number of synchronizing signals which are to be includedin the image interval but is smaller than a sum of the margin value andthe predetermined number.
 29. A video signal recording and/orreproducing method according to claim 24, further comprising a selectingstep for selecting an input video signal from a plurality of input videosignals.
 30. A video signal recording and/or reproducing methodaccording to claim 24, further comprising a step of alarming a user thata copy guard processing is applied to the input video signal.